Silicon nitride (SiN) is a widely used material in the manufacture of integrated circuits (ICs). Due to its low reactivity and high thermal stability, silicon nitride is used as an insulating material, a mask material, an etch-stop material, a barrier material, a spacer material, etc.
Techniques for forming SiN include physical vapor deposition (PVD) and chemical vapor deposition (CVD), such as high temperature thermal CVD, plasma-enhanced CVD (PECVD), low pressure CVD (LPCVD), or low temperature thermal atmospheric pressure CVD (APCVD). In one process, silane (SiH4) is reacted with ammonia (NH3) to form the SiN. Other silicon precursors may be used, such as silicon halides. Examples of silicon halides include silicon tetrachloride (SiCl4), dichlorosilane (SiCl2H2), trichlorosilane (SiHCl3), silicon tetraiodide (SiI4), HSiI3, H2SiI2, H3SiI, H2Si2I4, H4Si2I2, or H5Si2I. To produce high quality SiN, the PVD and CVD processes are conducted at a high temperature, usually greater than 750° C. However, these temperatures are not compatible with materials used in current ICs, some of which are thermally sensitive. Additionally, using a silicon halide as the silicon precursor is not desirable because reactive halide species, such as hydrochloric acid (HCl), are produced as byproducts. The reactive halide species are known to etch materials used in semiconductor fabrication, such as silicon-containing materials. The silicon halides are also known to degrade (e.g., corrode) equipment used in semiconductor fabrication.
Additional techniques for forming SiN on complex topographies have been developed as miniaturization of ICs continues. Atomic layer deposition (ALD) has been used to form SiN. The silane, silicon halide, and NH3 CVD precursors are sufficiently reactive at temperatures greater than 450° C. or in a plasma environment to form SiN by ALD. However, the precursors are not sufficiently reactive to be used at lower temperatures or without a plasma. While plasma-enhanced ALD (PEALD) has been used to form SiN, step coverage of the SiN is not sufficiently conformal to cover the complex topographies present in current ICs. PEALD precursors include H2n+2-y-z-wSinXyAzRw, where n is 1-10, y is 1 or more, z is 0 or more, w is 0 or more, X is iodine or bromine, and A is a halogen other than X, and R is an organic ligand. In addition, hydrogen is incorporated into the SiN, which decreases its desirable properties. Furthermore, excited species created during the plasma portion of the PEALD process are not selective to exposed materials on the ICs and, therefore, unintended reactions occur between the excited species and the exposed materials.
Amine-based precursors, such as bis(diethylamino)silane (BDEAS) and bis(tertiarybutylamino)silane (BTBAS), have also been investigated as ALD precursors to form SiN. However, reactions using these amine-based precursors have a high activation energy and, therefore, ALD of the SiN cannot be conducted at a low temperature.
SiI4 has also been used as a precursor to form SiN by ALD. While SiN is formed, the resulting SiN is not of sufficient quality to be used in ICs having complex topographies.
SiN formation becomes more complex as the size of ICs continues to decrease and the topographies become more challenging. As requirements for forming SiN become more stringent, the techniques mentioned above have not been able to form the SiN at the desired degree of conformality and at low temperatures.